Process for the production of alkyl and/or alkenyl oligoglycosides

ABSTRACT

The invention relates to an improved process for the production of alkyl and/or alkenyl oligoglycosides corresponding to formula (I): 
     
         R.sup.1 O- G!.sub.p                                        (I) 
    
     in which R 1  is an alkyl and/or alkenyl radical containing 4 to 22 carbon atoms, G is a sugar unit containing 5 or 6 carbon atoms and p is a number of 1 to 10, by acid-catalyzed acetalization of primary alcohols with monomeric carbohydrates, in which the reaction is carried out in a stirred tank reactor surmounted by a vacuum falling-film evaporator through which the mixture is pumped under reaction conditions.

This application is a 371 of PCT/EP95/03158, filed Aug. 9, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the production of alkyl and/oralkenyl oligoglycosides in which a combination of a stirred tank reactorand a falling-film evaporator is used.

2. State of Related Art

Alkyl oligoglycosides, more particularly alkyl oligoglucosides, arenonionic surfactants which are acquiring increasing significance byvirtue of their excellent detergent properties and their highecotoxicological compatibility. The production and use of thesecompounds have been described just recently in a number of synopticarticles, of which the articles by H. Hensen in Skin Care Forum, 1,(October 1992), D. Balzer and N. Ripke in Seifen-ole-Fette-Wachse 118,894 (1992) and B. Brancq in Seifen-ole-Fette-Wachse 118, 905 (1992) arecited as representative.

They are normally produced by acetalization of glucose with fattyalcohols in the presence of acidic catalysts. The catalyst is thenneutralized, excess fatty alcohol is removed and, if desired, theproduct is bleached.

There are numerous known processes for their production which arecharacterized by the use of certain units. For example, DE-A1 4 231 833(Huls) describes an acetalization reaction which is carried out as aliquid/liquid reaction in a thin-layer evaporator. Another process forthe production of alkyl glucosides, in which the acetalization reactionis carried out in an evaporator at an acid value of 1 to 10, is knownfrom EP-A1 0 501 032 (Huls). Finally, a process in which aqueous starchsirup is introduced into the reaction solution through an in-line mixeris known from WO 93/11143 (Henkel).

The discontinuous acetalization reaction is normally carried out instirred reactors which are equipped with a distillation head forremoving the water of condensation. Under laboratory conditions,substantially complete conversions can be obtained in short times, inaddition to which the reaction products are distinguished by a lowpolysugar content. However, scaling-up for industrial applicationinvolves difficulties. More particularly, it has been found that muchlonger reaction times are required for complete reaction of the glucose,resulting in an unwanted increase in secondary products, moreparticularly the polysugar content, quite apart from longer reactorpossession times.

Accordingly, the problem addressed by the present invention was toprovide an improved process for the production of alkyl glucosides whichwould be free from the disadvantages mentioned above.

DESCRIPTION OF THE INVENTION

The present invention relates to a process for the production of alkyland/or alkenyl oligoglycosides corresponding to formula (I):

    R.sup.1 O- G!.sub.p                                        (I)

in which R¹ is an alkyl and/or alkenyl radical containing 4 to 22 carbonatoms, G is a sugar unit containing 5 or 6 carbon atoms and p is anumber of 1 to 10, by acid-catalyzed acetalization of primary alcoholswith monomeric carbohydrates, in which the reaction is carried out in astirred tank reactor surmounted by a vacuum falling-film evaporatorthrough which the mixture is pumped under reaction conditions.

It has surprisingly been found that, by comparison with conventionalprocesses, pumping of the reaction mixture through a falling-filmevaporator enables equally high conversions of glucose to be obtained inshorter times and the polyglucose content to be reduced to levels which,normally, are only achieved in laboratory processes. The processaccording to the invention may be carried out discontinuously althoughit is preferably carried out continuously.

Alkyl and/or Alkenyl Oligoglycosides

Alkyl and alkenyl oligoglycosides are known materials which may beobtained by the relevant methods of preparative organic chemistry. EP-A10 301 298 and WO 90/03977 are cited as representative of the extensiveliterature available on the subject.

The alkyl and/or alkenyl oligoglycosides may be derived from aldoses orketoses containing 5 or 6 carbon atoms, preferably glucose. Accordingly,the preferred alkyl and/or alkenyl oligoglycosides are alkyl and/oralkenyl oligoglucosides. Powder forms of glucose, for example dextrosemonohydrate, are preferably used as starting materials.

The index p in general formula (I) indicates the degree ofoligomerization (DP degree), i.e. the distribution of mono- andoligoglycosides, and is a number of 1 to 10. Whereas p in a givencompound must always be an integer and, above all, may assume a value of1 to 6, the value p for a certain alkyl oligoglycoside is ananalytically determined calculated quantity which is generally a brokennumber. Alkyl and/or alkenyl oligoglycosides with an average degree ofoligomerization p of 1.1 to 3.0 are preferably used. Alkyl and/oralkenyl oligoglycosides with a degree of oligomerization below 1.7 and,more particularly, in the range from 1.2 to 1.4 are preferred from theapplicational point of view.

The alkyl or alkenyl radical R¹ may be derived from primary alcoholscontaining 4 to 11 and preferably 8 to 10 carbon atoms. Typical examplesare butanol, caproic alcohol, caprylic alcohol, capric alcohol andundecyl alcohol and the technical mixtures thereof which are formed, forexample, in the hydrogenation of technical fatty acid methyl esters orin the hydrogenation of aldehydes from Roelen's oxo synthesis. Preferredalkyl oligoglucosides are those with a chain length of C₈ to C₁₀ (DP=1to 3) which are obtained as the first runnings in the separation oftechnical C₈₋₁₈ coconut oil fatty alcohol by distillation and which maycontain less than 6% by weight of C₁₂ alcohol as an impurity and alsoalkyl oligoglucosides based on technical C_(9/11) oxoalcohols (DP=1 to3).

In addition, the alkyl or alkenyl radical R¹ may also be derived fromprimary alcohols containing 12 to 22 carbon atoms and preferably 12 to16 carbon atoms. Typical examples are lauryl alcohol, myristyl alcohol,cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol,oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, arachyl alcohol,gadoleyl alcohol, behenyl alcohol, erucyl alcohol and technical mixturesthereof which may be obtained as described above. Alkyl oligoglucosidesbased on hydrogenated C_(12/14) coconut oil fatty alcohol with a DP of 1to 3 are preferred.

Acetalization

The acetalization and working up of the reaction products are known perse. To establish the required degree of oligomerization, the alcoholsare used in a calculated excess. The molar ratio of fatty alcohol tosugar is normally 3:1 to 1:8 and is preferably in the range from 4:1 to5:1.

In addition to sulfuric acid and sulfuric acid semiesters--formed insitu--of the alcohols used, suitable catalysts are above allalkylbenzenesulfonic acid, p-toluenesulfonic acid, sulfosuccinic acidand other short-chain or long-chain aromatic or aliphatic sulfonic acidsor derivatives thereof, the catalysts being used in a concentration of0.1 to 5% by weight and preferably in a concentration of 0.5 to 3% byweight, based on the sum total of the starting materials.

In choosing the acetalization temperature, it is important to bear inmind that glucose decomposes rapidly at temperatures above 120° C.Accordingly, the reaction temperature is preferably in the range from100 to 110° C. while the pressure is in the range from 5 to 50 mbar.Under these conditions, the water of reaction can be continuouslydistilled off from the reaction equilibrium and the equilibrium shiftedonto the side of the target products.

Falling-Film Evaporators

Falling-film evaporators are evaporators in which evaporation takesplace from a thin layer with a thickness of typically 0.1 to 10 mm. Inthe most simple form, the liquid is distributed by trickling down. Aparticular form of falling-film evaporators are thin-layer evaporatorsin which the liquid is distributed by centrifugal forces or by rotatingfittings, for example wipers. The residence time of the products in theheated evaporator zone is typically between 0.1 and 30 s. Falling-filmevaporators which have an exchange surface of 1 to 30 and preferably 15to 25 m² /t reaction mixture are preferably used in the processaccording to the invention. The pumping rate is advantageously 1 to 20and preferably 5 to 15 t/h/t reaction mixture. The combination of areactor and thin-layer evaporator is particularly suitable forcontinuously carrying out glucosidation reactions, for example incascades of 2 to 4 reactors.

Commercial Applications

The alkyl and/or alkenyl oligoglycosides obtainable by the processaccording to the invention are distinguished by an advantageously lowpolysugar content and are suitable for the production of laundrydetergents, dishwashing detergents and cleaning products and alsohair-care and personal hygiene products, in which they may be present inquantities of 1 to 50% by weight and preferably in quantities of 5 to25% by weight, based on the particular product.

The following Examples are intended to illustrate a the inventionwithout limiting it in any way.

EXAMPLES Comparison Examples C1 to C3

Dextrose monohydrate and C_(12/14) coconut oil fatty alcohol (LOROLO®S,a product of Henkel KGaA, Dusseldorf, FRG) in a molar ratio of 1:5 wereintroduced into a stirred tank reactor equipped with a distillationhead, followed by the addition of 2% by weight of dodecylbenzenesulfonicacid as catalyst. The mixture was heated with stirring to 105° C. undera reduced pressure of 30 mbar, the water of condensation distilling offcontinuously. After all the water had been removed, the vacuum wasbroken and the mixture was cooled. The new catalyst was neutralized byaddition of magnesium oxide and sodium hydroxide solution and the excessfatty alcohol was removed in known manner in a two-stage distillationassembly using a falling-film evaporator and a thin-layer evaporator.The results are set out in Table 1.

Example 1

The procedure was as in Comparison Example 2, except that thecombination of the stirred tank reactor and the distillation head wasreplaced by a stirred tank reactor surmounted by a falling-filmevaporator with an exchange surface of 20 m² through which thesuspension was pumped at a rate of 20 t/h (corresponding to 10 t/h/treaction mixture). Working up was carried out as described above. Theresults are again set out in Table 1.

                  TABLE 1    ______________________________________    Characteristic data of the tests                                  Polyglucoside          Batch size   Reaction time                                  content    Ex.   kg           h          % by weight    ______________________________________    C1    2            4.5        2.5    C2    2,000        5.5        5.0    C3    20,000       6.5        6.0    1     2,000        4.5        2.7    ______________________________________

The expression "batch size" as used in Table 1 is understood to be thesum total of the starting materials fatty alcohol+glucose.

It can be seen that, in terms of reaction time and polyglucose content,the process according to the invention gives results which couldotherwise only be achieved under laboratory conditions.

We claim:
 1. A process for the production of alkyl and/or alkenyloligoglycosides corresponding to formula (I):

    R.sup.1 O-(G).sub.p                                        (I)

in which R¹ is an alkyl and/or alkenyl radical containing 8 to 22 carbonatoms, G is a sugar unit containing 5 or 6 carbon atoms and p is anumber of 1 to 10, comprising the steps of A) adding to a stirred tankreactor surmounted by a vacuum falling-film evaporatora) at least onealcohol containing from 8 to 22 carbon atoms, b) at least one monomericsugar containing 5 or 6 carbon atoms, and c) an acidic catalyst, to forma reaction mixture; and B) heating the reaction mixture to reactiontemperature and pumping the reaction mixture through the falling-filmevaporator at the reaction temperature.
 2. The process of claim 1wherein in step A) component a) is at least one primary alcoholcontaining from 8 to 10 carbon atoms.
 3. The process of claim 1 whereinin step A) component a) is at least one primary alcohol containing from12 to 22 carbon atoms.
 4. The process of claim 3 wherein the at leastone alcohol contains from 12 to 16 carbon atoms.
 5. The process of claim1 wherein in step A) component a) is technical C_(9/11) oxoalcohol. 6.The process of claim 1 wherein in step A) component a) is hydrogenatedC_(12/14) coconut oil fatty alcohol.
 7. The process of claim 1 whereinin step A) component b) is a glucose.
 8. The process of claim 7 whereinthe glucose is dextrose monohydrate.
 9. The process of claim 1 whereinin formula I, p=1 to
 6. 10. The process of claim 9 wherein p=1.1 to 3.0.11. The process of claim 10 wherein p=1.2 to 1.4.
 12. The process ofclaim 1 wherein in step A) components a) and b) are present in a molarratio of a): b) of from about 3:1 to about 8:1.
 13. The process of claim12 wherein the molar ratio is from about 4:1 to about 5:1.
 14. Theprocess of claim 1 wherein in step A) component c) isalkylbenzenesulfonic acid, p-toluenesulfonic acid, or sulfosuccinicacid.
 15. The process of claim 14 wherein component c) is present infrom about 0.1 to about 5% based on the sum of components a) through c).16. The process of claim 1 wherein the falling-film evaporator has anexchange surface of from about 1 to about 30 m² /t reaction mixture. 17.The process of claim 16 wherein the exchange surface is from about 15 toabout 25 m² /t.
 18. The process of claim 1 wherein in step B) thepumping rate is from about 1 to about 20 t/h/t reaction mixture.
 19. Theprocess of claim 18 wherein the pumping rate is from about 5 to about 15t/h/t.
 20. The process of claim 1 wherein in step B) the reactiontemperature is in the range of from about 100 to about 110° C., and thereaction pressure is in the range of from about 5 to about 50 mbar. 21.The process of claim 1 wherein in step A) component a) is a primaryalcohol or an oxoalcohol, and component b) is a glucose.
 22. The processof claim 21 wherein in formula I, p=1 to 6, and in step A) components a)and b) are present in a molar ratio of a): b) of from about 3:1 to about8:1.
 23. The process of claim 22 wherein in step A) component c) isalkylbenzenesulfonic acid, p-toluenesulfonic acid or sulfosuccinic acid,and component c) is present in from about 0.1 to about 5% based on thesum of components a) through c).
 24. The process of claim 22 wherein instep B) the reaction temperature is in the range of from about 100 toabout 110° C., and the reaction pressure is in the range of from about 5to about 50 mbar;the falling-film evaporator has an exchange surface offrom about 1 to about 30 m² /t reaction mixture; and in step B) thepumping rate is from about 1 to about 20 t/h/t reaction mixture.